The present invention relates to a multichip module provided with a light-emitting device such as an LED (light-emitting diode) or LD (laser diode) and an integrated circuit and designed for use in an electronic appliance or the like that exchanges data by infrared communication such as a PC (personal computer), PDA (personal digital assistant), DSC (digital still camera), or DVC (digital video cassette recorder).
A conventional multichip module provided with an LED and an LSI (large-scale integration) will be described. In FIG. 7, at (a) is shown a schematic view of a conventional multichip module provided with an LED 12 and an LSI 13, and at (b) is shown an equivalent circuit diagram thereof The LED 12, when a voltage is applied thereto, emits near-visible light such as infrared rays.
The LSI 13 is a monolithic integrated circuit having a circuit formed only on one side of a wafer. In the circuit diagram shown at (b) in FIG. 7, the monolithic LSI 13 is represented by a frame of broken lines. Within the frame of broken lines, only an output transistor, among other components incorporated in the monolithic LSI 13, is shown. This output transistor is an NPN-type bipolar transistor having a high driving capacity, and is inserted between the LED 12 and a reference potential. Here, the monolithic LSI 13 serves to control the amount of light emitted from the LED 12 by controlling the current flowing through the LED 12.
A metal lead frame 19 is constituted of island portions 14a and 14b for bonding chips such as the LED 12 and lead terminal portions 16 for external connection. Here, as shown at (b) in FIG. 7, neither of the cathode and the anode of the LED 12 is connected to a reference potential or a supplied voltage, and therefore the potential of the substrate thereof cannot be made equal to the potential of the substrate of the monolithic LSI 13. Thus, the LED 12 cannot be mounted on the same island portion as the monolithic LSI 13, and this is the reason that, as shown at (a) in FIG. 7, they are mounted on separate island portions 14a and 14b. 
The LED 12 and the monolithic LSI 13 are together sealed in a package 15 made of resin. In the circuit diagram shown at (b) in FIG. 7, reference numeral 17 represents a current limiting resistor that is either mounted externally via the lead terminal portions 16 of the lead frame or formed within the LSI 3.
When this multichip module 11 having the above-described structure is energized, the LED 12 emits light and simultaneously generates heat. This heat is first absorbed by the island portion 14a, which has a low heat resistance, and is then dissipated into air through the package 15.
In this multichip module 11 having the above-described structure, the monolithic LSI 13 is larger than the LED 12, and accordingly the island portion 14b for the monolithic LSI 13 is so formed as to be larger than the island portion 14a for the LED 12. Since the island portions 14a and 14b need to be formed within the package 15 having a limited size, it is inevitably impossible to secure a sufficiently large area for the island portion 14a for the LED 12.
As described above, the island portion 14a for the LED 12 first absorbs the heat of the LED 12 and then dissipates the heat into air through the package 15. However, the island portion 14a, which is thus smaller than is desired, cannot absorb sufficiently the heat of the LED 12, and accordingly the multichip module offers an unduly low package power (power dissipation capacity); that is, the LED 12 offers an unduly low heat capacity. This requires that the current flowing through the LED 12 be limited so as to restrict the amount of heat generated, and thus the amount of light emitted.
To achieve satisfactory dissipation of the heat of the LED 12, it is possible to form, for example, a heat dissipation fin on the island portion 14a. FIG. 8 is a schematic view of a multichip module as is realized by additionally forming heat dissipation fins 18a and 18b in the multichip module 11 described above. The heat dissipation fins 18a and 18b are formed integrally with the island portion 14a , with parts thereof protruding from the package 15. The heat dissipation fin 18a dissipates heat into air, and the heat dissipation fin 18b, which is so formed as to make contact with the printed circuit board (not shown) on which the multichip module 11 is mounted, dissipates heat through this printed circuit board.
Instead of providing heat dissipation fins 18a and 18b, it is also possible to make the package 15 itself larger so as to enlarge the island portion 14a for the LED 12 and thereby increase the heat capacity of the island portion 14a. 
However, forming a heat dissipation fin 18a or 18b or enlarging the package 15 inevitably makes the multichip module as a whole larger. This imposes extra limitations on the above-mentioned printed circuit board, or hinders miniaturization of electric appliances in which the multichip module is incorporated.
An object of the present invention is to provide a compact multichip module that offers a higher package power and that allows a satisfactorily large amount of light to be emitted from a light-emitting device.
To achieve the above object, according to the present invention, a multichip module is provided with: a light-emitting device having an anode electrode or a cathode electrode thereof connected to a supplied voltage or a reference voltage; a control circuit, having a substrate of an opposite conductivity type to the substrate of the light-emitting device, for controlling the electric current that is passed through the light-emitting device; a lead frame including an island on which both the light-emitting device and the control circuit are mounted; and a package for sealing the light-emitting device and the control circuit. In this structure, the heat that the light-emitting device generates as it emits light is absorbed by the lead frame, and is then dissipated therefrom into air through the package.